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Plant Cell Environ. 2018 Apr;41(4):809-822. doi: 10.1111/pce.13150. Epub 2018 Feb 22.

Two citrate transporters coordinately regulate citrate secretion from rice bean root tip under aluminum stress.

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State Key Laboratory of Plant Physiology and Biochemistry, College of Life Sciences, Zhejiang University, Hangzhou, 310058, China.
Key Laboratory of Tea Biology and Resources Utilization, Ministry of Agriculture, Tea Research Institute, Chinese Academy of Agricultural Sciences, Hangzhou, 310008, China.
Institute of Life Sciences, College of Life and Environmental Sciences, Hangzhou Normal University, Hangzhou, 310036, China.
Robert Holley Center for Agriculture and Health (USDA-ARS), Department of Plant Biology, Cornell University, Ithaca, NY, 14853, USA.
College of Resources and Environment, Yunnan Agricultural University, Kunming, 650201, China.
Global Institute for Food Security, University of Saskatchewan, Saskatoon, Saskatchewan, S7N 4J8, Canada.


Aluminum (Al)-induced organic acid secretion from the root apex is an important Al resistance mechanism. However, it remains unclear how plants fine-tune root organic acid secretion which can contribute significantly to the loss of fixed carbon from the plant. Here, we demonstrate that Al-induced citrate secretion from the rice bean root apex is biphasic, consisting of an early phase with low secretion and a later phase of large citrate secretion. We isolated and characterized VuMATE2 as a possible second citrate transporter in rice bean functioning in tandem with VuMATE1, which we previously identified. The time-dependent kinetics of VuMATE2 expression correlates well with the kinetics of early phase root citrate secretion. Ectopic expression of VuMATE2 in Arabidopsis resulted in increased root citrate secretion and Al resistance. Electrophysiological analysis of Xenopus oocytes expressing VuMATE2 indicated VuMATE2 mediates anion efflux. However, the expression regulation of VuMATE2 differs from VuMATE1. While a protein translation inhibitor suppressed Al-induced VuMATE1 expression, it releases VuMATE2 expression. Yeast one-hybrid assays demonstrated that a previously identified transcription factor, VuSTOP1, interacts with the VuMATE2 promoter at a GGGAGG cis-acting motif. Thus, we demonstrate that plants adapt to Al toxicity by fine-tuning root citrate secretion with two separate root citrate transport systems.

[Indexed for MEDLINE]

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